The disclosed systems and methods relate to nuclear magnetic resonance (NMR) testing and more particularly to NMR spectrometers probes.
Nuclear magnetic resonance (NMR) testing of substances to determine the constituents therein is well known in the art. In known devices, the sample can be arranged between the poles of a magnet and enclosed by a wire coil to enable a sample to be subjected to RF electromagnetic pulses of a predetermined frequency. The resulting NMR pulse generated by the nuclei of the sample under test can be detected and processed by the NMR device in a well-known manner to identify the sample constituents.
NMR analysis can be performed in devices commonly known as spectrometers. These spectrometers can have a probe that accepts the sample to be analyzed between poles of a magnet. The RF coils and tuning circuitry associated with the probe can create a magnetic field (B) that rotates the net magnetization of the nucleus. These RF coils also detect the transverse magnetization as it precesses in the X,Y plane. The RF coil can pulse the sample nucleus at the Lamor frequency to generate a readable signal for sample identification. An exemplary probe is disclosed in commonly owned U.S. Pat. No. 5,371,464 (Rapoport), and is incorporated herein by reference in its entirety. This probe and others like it, while an improvement in the art, still have several disadvantages.
A disadvantage of some probes includes the failure to react or respond to temperature changes of the sample, and particularly temperature increases caused by a sample where such temperature increases heat the magnet because of the strong thermal conductivity between the sample stream and the magnet. Samples are often presented to the probe at high temperatures to remain liquid for analysis, and to avoid gelling, solidifying or the like, if cooled. A sample can dissipate from within the probe and transfer to the ambient environment to ultimately reach the magnet and raise (or lower) the magnet's temperature. Heat from the sample may also be transferred by radiating through the ambient environment, and the sample temperature can be conducted through the probe material.
Since magnetic flux is proportional to magnet temperature, the magnet, upon heating (or other change of temperature) can undergo flux changes. These changes in flux can alter the homogeneity of the magnet, and thus the NMR results can be inaccurate, and in some cases, worthless.
Even a small change in sample stream temperature can be sufficient to cause a measurable change in magnetic flux. Frequency locks, such as that disclosed in U.S. Pat. No. 5,166,620 (Panosh), incorporated herein by reference in its entirety, can be introduced into probes to counter changes in flux, by controlling the frequency of the RF coils. As for changes in magnetic homogeneity, these can be made by shimming the magnet.
Currently, when magnet control is desired complex heat exchangers can be employed and placed in the path of the sample stream prior to its entry into the probe. This can be extremely costly and difficult to implement in in-line process environments.
Additionally, the temperature conductivity between the magnet and the sample stream can affect the sample itself. With the sample forced to remain in the probe for the desired testing time (period), the sample can change as its flow temporarily ceases during the analysis period. This temperature change can also affect the magnetic field and compromise NMR measurements.
Another aspect of the invention relates to another disadvantage of the common use of probes. In laboratory-related uses, changing samples, therefore changing probes, is often required. It is known that specimen probes may break during the changing process. Once this happens there is the need to disassemble the probe body from the machine in order to clean it and, in a worst case scenario, repair it in case that the spills caused any damage to the parts.